In inductive power transfer (IPT) systems, power is transferred inductively between a primary conductive path or track supplied by an alternating-current power supply (the power supply and track together forming a primary side of the IPT system), and one or more pick-ups inductively coupled with the track (forming the secondary side of the system).
The pick-up comprises a tuned or resonant circuit consisting of at least a pick-up coil and a tuning capacitor. Two common pick-up topologies are the series-tuned pick-up, in which the tuning capacitor is provided in series with the pick-up coil, and the parallel-tuned pick-up, in which the tuning capacitor is provided in parallel with the pick-up coil. The tuned circuit is typically electrically coupled to a control circuit (typically comprising a rectifier and a converter or regulator) to obtain the desired output to supply a load.
An alternative pick-up topology is known as the series-parallel tuned LCL (inductor-capacitor-inductor) pick-up, as shown by way of example in FIG. 1.
The series-parallel tuned LCL pick-up topology (hereinafter referred to as an LCL pick-up) is controlled with a slow switching (i.e. a switching frequency that is much less than the frequency of the IPT track) decoupling control method similar to a slow switching parallel-tuned pick-up. An issue with the slow switching topology is the transient inrush power drawn by the pick-up during normal power regulation. In multiple pick-up systems, each time the pick-up is switched on the transient power inrush transiently reduces the track current. This disturbance, if large, will limit the power flow to all other pick-ups coupled to the track. A control circuit topology for minimizing this track current transient disturbance using a parallel LC tuned pick-up controller was described by Boys, J. T.; Chen, CI; Covic, G. A.; “Controlling inrush currents in inductively coupled power systems,” The 7th International Power Engineering Conference, 2005, Vol. 2, pp. 1046-1051, Nov. 29, 2005-Dec. 2, 2005. However, this simple approach cannot be used in the LCL topology using existing design approaches because it requires a large DC inductor for continuous current conduction in the switch mode circuit.